Security officials advised the speaker not to convene the session and evacuated the building after the dogs started barking at a patch of newly laid carpet.

Iddawela did not specify what the security threat was. A security official said nothing was found when the carpet was removed and speculated that the dogs may have smelled sulphur - a chemical also used in explosives - in the adhesive used to attach it to the floor. He spoke on condition of anonymity, because he is not authorised to speak publicly to the media.

The scare came amid increased tensions between the government and the Tamil Tiger rebels after the reported disappearance or abduction of 10 ethnic Tamils working for a relief agency affiliated with the group. The Tigers have threatened to pull out of forthcoming peace talks unless the government does more to protect Tamils. Two of those allegedly abducted have returned home and police are trying to find the others.

The Tamil Tigers want to create a separate homeland for Sri Lanka's 3.2 million minority Tamils. Before the government and the rebels signed a ceasefire in 2002, anti-aircraft guns were deployed outside parliament to protect against any rebel attacks.

Parliament was last attacked in 1987 when an employee lobbed a grenade that killed a district minister and wounded several others. There was no political motive.

Parliament is protected by police officers from an elite Special Task Force unit.